The present invention relates to a foot force sensing insole worn inside of a person's shoe and capable of sensing varying compressive force exerted by a person's foot at different points along the foot and transducing the compressive force into electrical signals suitable for transmission to computerized processes, monitoring and analyzing systems for detection, diagnosis, characterization, gait analysis, feedback for automatic control of electrical stimulation devices and substitute sensory feedback.
Individuals with impaired functions of the lower extremity are limited in their abilities to stand, to negotiate curbing and stairs, and to walk. These disabilities often reduce physical access to certain locations, restrict employment opportunities and lower the quality of life. Functional electrical stimulation (FES) technology used alone or in conjunction with orthoses (bracing) provides selective electrical stimulation of nerves and/or muscle allowing some of the above mentioned individuals to stand, walk, maneuver and climb stairs. However, current lower extremity FES systems do not have a sufficient artificial sensory feedback to allow detection of time of foot strike, total force, or center of pressure (center of compressive force) or changes thereto. Essential to the successful and practical application of such systems is an economical, easy to use, reliable, accurate, highly mobile and unobtrusive sensory device which provides a neuroprosthetic sensory input. It is imperative for applications involving insensate feet that the device not only be very thin, lightweight, and allow for mobility; but also be able to detect small changes in the amount of compressive force exerted by the foot on a continuous basis.
There are a number of insole foot force sensing devices currently used for measuring force on the foot. For example, U.S. Pat. No. 4,745,930 discloses a flexible force sensing insole which incorporates multiple electrical switches which close after a certain threshold level of force is imposed on the insole. U.S. Pat. No. 5,033,291 discloses a force sensing device which utilizes a plurality of intersecting electrodes. The electrodes act as open circuit switches at each intersection which close when force is applied to the insole at that intersection location. The resistance between the two electrodes varies with the amount of force applied. U.S. Pat. No. 4,426,884 discloses a flexible force sensor which acts as an open circuit, closing with the application of force on the sensor and having resistance that varies with the amount of force.
While these devices maybe useful in systems used for testing, monitoring and analyzing a person's gait, particularly in laboratory environments, they were not designed as a neuroprosthetic sensory input. Accordingly, a need exists for a foot force sensor which allows for effective application with neuroprosthetic systems.